Congenital and inherited polycystic renal disorders are among the most frequent primary diagnoses in children with chronic kidney disease and are responsible for 15% of renal transplants. Inherited polycystic kidney diseases (PKD) of childhood include nephronophthisis, autosomal recessive polycystic kidney disease and medullary cystic kidney disease. Nephronophthisis is the most common cause of end stage renal disease in children and young adults and the infantile form (NPHP2) has recently been linked to mutations in the inv gene. The function of inversin, the inv gene product, is not known. We developed antibodies to inversin that localized to plasma membranes, nuclei, perinuclear cytoplasm and primary cilia, and co-immunoprecipitated with proteins involved in junctional complexes, axis development and PKD, i.e. N-cadherin and beta-catenin. We found fusiform cysts in proximal tubules and collecting ducts of inv/inv mice. Cilia are implicated in the formation of renal cysts and many PKD-associated proteins have been localized to cilia, including polaris, cystin and polycystins-1 and -2. We propose to define the function of inversin by determining its interaction with other PKD-associated proteins. Our long-term objective is to determine how defective proteins in cilia or plasma membranes lead to PKD so that therapeutic modalities may be developed. Our immediate objective is to establish the molecular and cellular basis of PKD by investigating the functional relationship of inversin with known PKD-associated proteins including the polycystins, cadherins and catenins. We hypothesize that inversin interacts with the polycystins, cadherins and catenins in normal development and maturation of renal epithelium. This interaction allows renal epithelial cells to progress through developmental checkpoints by integrating junctional complexes with cilia. Our general strategy is to study the potential role of inversin in the multi-protein polycystin/PKD complex by applying techniques of functional genomics to established culture model systems. We propose one overall specific aim with two components. First, we will determine the structural and functional significance of inversin in renal development by blocking in vitro translation of inversin in cultured renal epithelial cells and transfilter embryonic kidney cultures. Second, we will identify crucial binding partners of inversin in these cultured systems by blocking in vitro translation and assaying for changes in PKD-associated proteins.